1. Field of the Invention
This invention constitutes an improved means and method for excising plaque from stenoses in human arteries including those which have an eccentrically located lumen by employing the method termed Vacuum Pullback Atherectomy (VPA) and using the Shielded Pullback Atherectomy Catheter (SPAC).
2. Description of the Prior Art
U.S. Pat. No. 4,765,332 entitled "Pullback Atherectomy Catheter System" which issued on Aug. 23, 1988 to R. E. Fischell and T. A. Fischell and is incorporated herein by reference teaches an atherectomy catheter that cuts in the retrograde direction. The design taught by the Fischells is however not well suited to excise plaque from highly eccentric stenoses. Furthermore, the U.S. Pat. No. 4,765,332 patent does not teach any way to excise plaque so that the final luminal diameter of the stenosis undergoing atherectomy is larger than the diameter of the catheter's distal end.
U.S. patent application Ser. No. 577,633, now U.S. Pat. No. 5,127,902 by Robert E. Fischell filed on Sep. 5, 1990 and entitled "Apparatus and Method for Precisely Controlling the Excision of Obstructive Tissue in a Human Blood Vessel" which is incorporated herein by reference, is an improvement in the atherectomy art in that it describes a means and method for excising plaque so that the final luminal diameter of the stenosis is larger than the diameter of the catheter's distal end. However, this cited patent application teaches an atherectomy means and method which requires a pressure cuff to be applied externally to the limb of the body being treated. Thus, deep internal arteries such as coronary arteries which cannot readily have a pressure cuff placed around the surrounding tissue are not able to be treated using the invention taught in that patent application.
In 1989, B. F. Waller, M.D. authored an article entitled "The Eccentric Coronary Atherosclerotic Plaque: Morphologic Observations and Clinical Relevance" which states that 73% of 500 coronary artery stenoses that he studied had an eccentric lumen. Dr. Waller defines an eccentric stenosis as one in which at least some arc length of the arterial wall is not significantly thickened with plaque. Of the 365 coronary arteries with eccentric stenoses that Dr. Waller studied, he reported that the arc length of disease-free wall measured from 2.3% to 32% of the vessel circumference with a mean of 16.6%. This corresponds to angular arcs of 8.degree. minimum, 115.degree. maximum and 60.degree. mean arc length.
From Dr. Waller's careful studies it becomes apparent that for most cases of atherectomy of the coronary arteries it is highly desirable to have an atherectomy catheter that would shield this arc of disease-free wall while excising the plaque that is attached to the remaining arc of the diseased arterial wall.
Some of the earliest prior art that addresses the problem of atherectomy of both concentric and eccentric stenoses is the European Patent Application 0,163,502 entitled "Atherectomy Device and Method" by J. B. Simpson having a priority date of May 5, 1984. This Simpson patent application teaches an anterograde cutter on a flexible cable that moves within a generally cylindrical housing having a rounded metallic distal end. The housing has a longitudinally extending cutout which typically makes up an arc of approximately 90.degree.; i.e. the rigid metal portion of the housing is shown to have an arc of approximately 270.degree.. A balloon is secured to the housing opposite the cutout. When the balloon is inflated, the cutout is pressed into the plaque on the opposite side of the arterial wall. This makes it possible for the rotating, anterograde sliding cutter to shave off the plaque and push it into a plaque collection chamber located within the distal, rounded end of the housing. Although the design taught by Simpson in this European Patent Application has been successfully used to excise plaque from human arteries, it has several significant shortcomings especially when used in tortuous coronary arteries. Brief descriptions of the deficiencies of this Simpson design are as follows:
(1) The rigid, rounded distal end of the housing is not an efficient shape for Dottering (pushing) through a tight stenosis and does not track well over a guide wire. PA0 (2) For the over-the-wire design illustrated in FIGS. 1, 2, and 3 of the Simpson Application, the guide wire passes through the plaque collection chamber. Thus, plaque is packed into the plaque collection chamber tightly around the guide wire. Therefore, the guide wire becomes locked into the plaque, and therefore, the guide wire must be removed when the catheter is removed. This is a significant operational shortcoming of this structural design because placing the catheter back into the artery also requires replacing and repositioning the guide wire. PA0 (3) The embodiment showing a fixed guide wire at the housing's distal end (FIG. 7), will of course, also require the guide wire to be removed from the artery when the catheter is removed. This is a disadvantageous design as compared to an over-the-wire system (not however as implemented in the Simpson design) in which the guide wire can remain in place while the catheter is pushed in and/or out one or more times into the artery that is undergoing atherectomy. PA0 (4) Since some coronary arteries exhibit considerable tortuosity, it is highly desirable to minimize the rigid length (and therefore the volume) of the housing while maximizing the length of the plaque collection chamber. The Simpson design is disadvantageous in that it teaches a comparatively long rigid housing with only a very short length devoted to storage of the cut plaque. PA0 (5) Because the cutter pushes in the anterograde direction (as opposed to the retrograde direction) the force that can be exerted by the flexible cable is limited. PA0 (6) The comparatively sharp metal edges of the housing cutout are disadvantageous because they make it more difficult to Dotter through a long, tight stenosis. This is because these sharp metal edges can be caught in a tight stenosis and prevent passage of the distal end of the catheter. Furthermore, this design prevents easy passage of the housing cutout through the proximal valve of an introducer sheath which is another significant disadvantage. PA0 (7) Because the cutter is on a flexible cable, the cutout must be considerably less than 180.degree. in arc or else the cutter could pop out of the housing as it slides forward in the anterograde direction for example when the cutter would engage some calcified plaque. This limits the arc of plaque that can be cut on any single forward cutting pass of the cutter. Thus, with a 90.degree. arc of the cutout, the housing must typically be rotated at least four times around its longitudinal axis in order to collect plaque around all 360.degree. of arc around the arterial wall. This makes for a comparatively time consuming and arduous atherectomy. PA0 (8) The plaque must first be collected in the cutter and then transferred to the plaque collection section of the housing. This design is comparatively complex when compared to simply collecting the plaque within the cutter itself and leaving it there. PA0 (9) The inflatable balloon which is taught in the Simpson design adds to the catheter's complexity, increases the effective diameter at the catheter's distal end and decreases system reliability because it may fail to inflate or deflate or it may burst. Furthermore, balloon inflation can cause intimal dissection of the artery which is clearly an undesirable outcome of atherectomy. PA0 (10) The sharpened edge of the cutter can engage the metal, distal interior portion of the housing while spinning and therefore can become dull after a single usage. This is disadvantageous when, as is typically necessary, repeated cuts are required. PA0 (1) A flexible guide wire, PA0 (2) A cut/collect catheter having a central passageway through which the guide wire can be passed, PA0 (3) A shielding catheter which moves concentrically and slideably along the cut/collect catheter, and PA0 (4) A rotating means attachable at the cut/collect catheter's proximal end which can rotate the cut/collect catheter as it is being pulled back in the retrograde direction. PA0 1. A vacuum source attachable at the shielding catheter's proximal end to one lumen which is in fluid communication with an opening at the shielding catheter's distal end, and PA0 2. A source of an inflation fluid which is attached at the shielding catheter's proximal end to a second lumen of the shielding catheter which is in fluid communication with an occlusive balloon located at the shielding catheter's distal end.
Two additional prior art patents, namely U.S. Pat. No. 4,669,469 by H. S. Gifford, III and J. B. Simpson and U.S. Pat. No. 4,781,186 by J. B. Simpson et al, teach art comparable to that taught in the above referenced European Patent Application by J. B. Simpson. Each of these two U.S. patents have virtually all the shortcomings described in items (1) through (10) inclusive above.